Summary form only given. The experiment consists of a Sr vapor cell magneto optical trap (MOT). Since for laser-cooled alkaline earth atoms the even isotopes have no hyperfine structure, they provide an ideal system for testing Doppler-cooling theory. (Alkali atoms are subject to sub-Doppler cooling mechanisms.) We have measured the spring constant (k) and damping coefficient (/spl alpha/) in a strontium MOT by observing the damped oscillation response of the trapped atom location to a square-wave chopped pushing beam.
Summary form only given. The experiment consists of a Sr vapor cell magneto optical trap (MOT). Since for laser-cooled alkaline earth atoms the even isotopes have no hyperfine structure, they provide an ideal system for testing Doppler-cooling theory. (Alkali atoms are subject to sub-Doppler cooling mechanisms.) We have measured the spring constant (k) and damping coefficient (/spl alpha/) in a strontium MOT by observing the damped oscillation response of the trapped atom location to a square-wave chopped pushing beam.
Alkaline-earth-metal atoms present an ideal platform for exploring magneto-optic trap (MOT) dynamics, enabling unique and definitive tests of laser cooling and trapping mechanisms. We have measured the trapping beam intensity, detuning, magnetic-field gradient, trap density, and lifetime dependence of the spring constant $\ensuremath{\kappa}$ and damping coefficient $\ensuremath{\alpha}$ for a ${}^{1}{S}_{0}{\ensuremath{-}}^{1}{P}_{1}$ 88Sr MOT by fitting the oscillatory response of the atom cloud to a step-function force. We find that the observed behavior of $\ensuremath{\kappa}$ and $\ensuremath{\alpha}$ provide a unified and consistent picture of trap dynamics that agrees with Doppler cooling theory at the level of 10 Additionally, we demonstrate that the trapped atom temperature can be determined directly from measured value of $\ensuremath{\kappa}$ and the trap size, in excellent agreement with free-expansion temperature measurements. However, the experimentally determined temperature is much higher than Doppler cooling theory, implying significant additional heating mechanisms.
We present a detailed investigation of strontium magneto-optical trap (MOT) dynamics. Relevant physical quantities in the trap, such as temperature, atom number and density, and loss channels and lifetime, are explored with respect to various trap parameters. By studying the oscillatory response of a two-level 1S0–1P1 88Sr MOT, we firmly establish the laser cooling dynamics predicted by Doppler theory. Measurements of the MOT temperature, however, deviate severely from Doppler theory predictions, implying significant additional heating mechanisms. To explore the feasibility of attaining quantum degenerate alkaline-earth samples via evaporative cooling, we also present the first experimental demonstration of magnetically trapped metastable 88Sr. Furthermore, motivated by the goal of establishing the fermionic isotope 87Sr as one of the highest-quality, neutral-atom-based optical frequency standards, we present a preliminary study of sub-Doppler cooling in a 87Sr MOT. A dual-isotope (87Sr and 88Sr) MOT is also demonstrated.
ABSTRACT In a ceramic vapor cell we have created a robust Sr magneto-optical trap that stores about 108 atoms with lifetimes>200 ms. We eliminate the 5p 1P14d 1D2*5p 3P2 leak and achieve a 10-fold improvement in trap lifetime byrepumping the 5p 3Po,2 dark states with 679 nm and 707 nm light. The observed lifetime is now limited by coldcollision losses, and we have preliminary measurements of the 2-body loss rate. Direct readout of the trap velocity distribution is possible using the narrow (7 kHz) 52 'S0----5p 3P1 intercombination line at 689 nm. We can also cool with this narrow transition and have achieved a 40-fold 1-D velocity compression for about 5% of the trapped atoms by applying this second-stage cooling. Keywords: Laser cooling, laser trapping, alkaline earths, cold collisions, frequency metrology 1. INTRODUCTION Laser cooling and trapping techniques have advanced to become an important tool of the atomic physics community, and in recent years there has been considerable interest in expanding the range of trapped elements. The alkalineearths, in particular, possess unique characteristics which make them interesting to trap. Studies of long-rangeatom-atom interactions are simplified because they have no hyperfine structure, and their narrow intercombinationtransitions make them excellent candidates for optical frequency standards. Furthermore, Doppler cooling with thesenarrow transitions can reduce temperatures to near the recoil limit.The most abundant alkaline earth isotopes have I =
We have measured the low-density characteristics of a magneto-optical trap for both isotopes of rubidium. Trapped-atom temperatures are measured by the time-of-flight technique and are similar to temperatures in optical molasses. They are below the Doppler limit in most cases and increase linearly with the ratio of laser intensity to laser detuning. A slight difference between the two isotopes is observed. The data agree well with three-dimensional, multistate, semiclassical simulations. Spring constants of the trap are inferred from careful measurements of the size of the trapped-atom cloud. The spring constant is seen to increase with intensity at low intensity, becoming independent of intensity at high intensity. This trend is consistent with sub-Doppler cooling mechanisms.
The isotope selectivity of the strontium (Sr) magneto-optical trap (MOT) is measured by a time-of-flight (TOF) mass spectrometer. The thermally generated Sr atoms are slowed down by the Zeeman slowing technique and trapped by the magneto-optical method. The trapped atoms are photoionized by the nonresonant two-photon ionization, and the generated ions are analyzed by the TOF mass spectrometer. The isotope selectivity of the MOT is up to approximately 2000 for 86Sr, and the overall selectivity of the system, which consists of the MOT and the mass spectrometer is also discussed.
We developed a magneto-optical trap reaction microscope (MOTREMI) for strontium atoms by combining multiparticle coincident detection with the laser cooling technique. The present compact injection system enables the production of cold Sr atoms in three modes of two-dimensional (2D) magneto-optical trap (MOT) beam, molasses, and three-dimensional (3D) MOT, providing adjustable densities and ratios of the ground state 5s2 (1S0) and the excited states 5s5p1P1 and 3PJ. The target profiles including temperature, density, and size of the 3D MOT as well as the 2D MOT beam cold atomic flux were characterized in detail. Using the present setup, we investigate the single photoionization of Sr atoms with molasses through few-photons absorption in 800 nm, where Sr+ and ${e}^{\ensuremath{-}}$ are detected in coincidence and most of the ionization channels are identified. The momentum resolution for coincident Sr+ and ${e}^{\ensuremath{-}}$ along time-of-flight direction are achieved up to 0.12 a.u. and 0.02 a.u., respectively. The spectra of photoelectron ionized from the ground state as well as several excited states show distinct structures manifesting prominent contributions from multiphoton absorption. Detecting complete vector momenta of electrons and recoil ions in coincidence paves a way for further investigation of two-electron correlation dynamics and multielectron effects with alkaline-earth atoms.